Vaso-occlusive devices or implants are used for a wide variety of reasons, including treatment of intra-vascular aneurysms. A common vaso-occlusive device takes the form of a soft, helically wound coil formed by winding a platinum (or platinum alloy) wire strand about a primary mandrel. The relative stiffness of the coil will depend, among other things, on its composition, the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. The coil is then wrapped around a larger, secondary mandrel, and again heat treated to impart a secondary shape. For example, U.S. Pat. No. 4,994,069, issued to Ritchart et al., describes a vaso-occlusive coil that assumes a linear, helical primary shape when stretched for placement through the lumen of a delivery catheter, and a folded, convoluted secondary shape when released from the delivery catheter and deposited in the vasculature.
In order to deliver the vaso-occlusive coils to a desired site, e.g., an aneurysm, in the vasculature, it is well-known to first position a small profile, micro-catheter at the site using a steerable guidewire. Typically, the distal end of the micro-catheter is provided, either by the attending physician or by the manufacturer, with a selected pre-shaped bend, e.g., 45°, 90°, “J”, “S”, or other bending shape, depending on the particular anatomy of the patient, so that it will stay in a desired position for releasing one or more vaso-occlusive coil(s) into the aneurysm once the guidewire is withdrawn. A delivery or “pusher” wire is then passed through the micro-catheter, until a vaso-occlusive coil coupled to a distal end of the pusher wire is extended out of the distal end opening of the micro-catheter and into the aneurysm. The vaso-occlusive device is then released or “detached” from the end pusher wire, and the pusher wire is withdrawn back through the catheter. Depending on the particular needs of the patient, another occlusive device may then be pushed through the catheter and released at the same site.
One known way to release a vaso-occlusive coil from the end of the pusher wire is through the use of an electrolytically severable junction, which is a small exposed section or detachment zone located along a distal end portion of the pusher wire. The detachment zone is typically made of stainless steel and is located just proximal of the vaso-occlusive device. An electrolytically severable junction is susceptible to electrolysis and disintegrates when the pusher wire is electrically charged in the presence of an ionic solution, such as blood or other bodily fluids. Thus, once the detachment zone exits out of the catheter distal end and is exposed in the vessel blood pool of the patient, a current applied to the conductive pusher wire completes a circuit with an electrode attached to the patient's skin, or with a conductive needle inserted through the skin at a remote site, and the detachment zone disintegrates due to electrolysis.
U.S. Pat. No. 5,122,136 issued to Guglielmi, et al. discloses a device in which a portion of the guidewire connected between the tip and the body of the guidewire is comprised of stainless steel and exposed to the bloodstream so that upon continued application of a positive current to the exposed portion, the exposed portion is corroded away at least at one location and the tip is separated from the body of the guidewire. The guidewire and a microcatheter are thereafter removed leaving the guidewire tip embedded in the thrombus formed within the vascular cavity.
One perceived disadvantage with vaso-occlusive devices that are deployed using electrolytic detachment is that the electrolytic process requires a certain amount of time to elapse to effectuate release of the vaso-occlusive element. This time lag is also a perceived disadvantage for vaso-occlusive delivery devices that utilize thermal detachment mechanisms. U.S. Pat. No. 6,966,892 issued to Gandhi, et al. discloses a vaso-occlusive device that uses a thermal detachment system.
Another detachment modality used to deploy vaso-occlusive elements uses mechanical detachment. U.S. Pat. No. 5,800,453 issued to Gia discloses embolic coils that have a receiving slot on one end. A catheter control wire or pusher guidewire having a hook which engages the coil's receiving slot is used as a coil pusher to eject the coil at the chosen site. The coils may also be placed within the lumen with a catheter in a nose-to-tail fashion and pushed into the body lumen. Pushing the coil assembly via the pusher from the distal end of the catheter body uncouples the distal most coil.
Another example of a mechanical detachment system is disclosed in U.S. Pat. No. 5,800,455 issued to Palermo et al. Palermo et al. discloses a delivery system that includes a coil having a clasp located at one end. The clasp includes a passageway for a control wire. The clasp interlocks with another clasp located on a distal end of a pusher member. The control wire is withdrawn in the proximal direction to release the coil.
Still other mechanical detachments systems have been proposed that use a fiber segment that is pulled in the proximal direction to decoupled the fiber from the embolic coil device. Examples of these systems may be found in U.S. Patent Application Publication Nos. 2006/0025803 A1 (coiled fiber), 2006/0025802 A1 (U-shaped fiber), and 2006/0025801 A1 (detachment filament).
One problem with certain existing mechanical detachment systems is that the junction between the embolic element and the releasing member moves during the detachment process which may adversely impact the placement of the embolic element within the aneurysm. Another complication is that mechanical detachment systems tend to have a stiff main section that complicates accurate placement of the delivery system at the desired location, i.e., a stiff section of the pusher wire or the pusher wire/coil junction can cause a pre-shaped micro-catheter to kick back or recoil from the aneurysm. Mechanical detachment systems also are perceived by physicians as being harder to use than other devices. In addition, certain mechanical detachment systems may jeopardize the integrity of the embolic element (e.g. coil) after detachment.
There thus is a need for a vaso-occlusive delivery system that utilizes mechanical detachment yet does not suffer from the aforementioned deficiencies. Such a system should be easy to use yet provide for consistent detachment of embolic elements in the desired location. Moreover, the delivery system should be able to release the embolic element without extensive movement resulting from the detachment operation.